1. Field of the Invention
This invention relates to a washing process in which the concentration of the wash liquor is determined by analysis.
2. Discussion of Related Art
In the machine washing of laundry, it is desirable, above all in the institutional sector, completely or partly to automate dosage of the detergent in the preparation or regeneration of the wash liquor. To control dosage according to requirements, it has proved to be useful to employ not only external parameters, but also the actual concentration of washing-active substance in the liquor as a guide for subsequent dosage of the detergent. The necessary dosage is thus the difference between the required concentration and actual concentration of washing-active substance. Control methods such as these are today mainly used in batch washing machines, the fact that the total conductivity of the liquor increases with increasing concentration being used to determine the content of washing-active substance in the liquor. The connection between conductivity and concentration of washing-active substances has to be empirically determined for each new composition of a detergent. With this system, difficulties arise out of the highly variable input of electrolytes with the soiled washing which leads to inaccurate analysis results and hence to incorrect dosage. In addition, DE-OS 29 49 254 describes a process in which the concentration of wash liquors and cleaning solutions is photometrically determined through the content of fluorescent dyes. The disadvantage of this process lies in the tendency of all dyes to be adsorbed onto textile fibers from solution so that the wash liquor loses these dyes more quickly than the other active substances. Since, in addition, dye adsorption also depends on the quality of the fibre material, the concentration of washing-active substances cannot be reliably determined in this way. Accordingly, for more reliable dosage of the detergent, efforts have long been made to find a process which would not be affected by such factors.